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Note for Hydraulics and Hydraulic Machinery - HHM By JNTU Heroes

  • Hydraulics and Hydraulic Machinery - HHM
  • Note
  • Jawaharlal Nehru Technological University Anantapur (JNTU) College of Engineering (CEP), Pulivendula, Pulivendula, Andhra Pradesh, India - JNTUACEP
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Text from page-2

Governors for Turbines Rated Speed Lever T o w a r d s t u r b i n e To Reduce Speed Rated Speed To increase Speed g u i d i n g Pendulum or actuator To Reduce Speed fulcrum mechanis m From turbine shaft To increase Speed Distribution valve Gear Pump Oil Sump Servomotor or relay cylinder Oil pressure governor A Governor is a mechanism to regulate the speed of the shaft of a turbine. The turbine is coupled to the shaft of the generator, which is generating power/electricity. The power generated should have uniform rating of current and frequency which in turn depends on the speed of the shaft of the turbine. Fig shows the oil pressure governor for a turbine. The main component parts of the governor are: 1. The servomotor or Relay cylinder 2. The distribution valve or control valve 3. Actuator or Pendulum 4. Oil Sump 5. Gear pump which runs by tapping power from the power shaft by belt drive 6. A pipe system communicating with the control valve, servomotor and the sump When the turbine is subjected to its normal load, it runs at the normal speed N. When the load on the turbine increases or decreases the speed of the turbine also will accordingly decrease ot increase. The oil pressure governor will restore the speed to the normal value. The normal position of the governor at the normal speed is shown in fig.

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As the load on the turbine increases, the speed decreases in turn reducing the speed of the vertical bar of the governor. The fly balls of the centrifugal governor are brought to a lower level, thereby bringing the displacement lever downward. This through the fulcrum lifts the piston of the control valve and thereby opens the valve A and closes the valve B. Oil is pumped through valve A and into the servomotor, thereby pushing the piston of the servomotor backwards. This in turn increases the inlet area of the discharge into the turbine, thereby increasing the speed. Similarly, with decrease in load on the turbine, the fly balls move farther away from the vertical shaft of the governor, thereby lifting the displacement lever upwards. This through the fulcrum lowers the piston of the control valve and thereby opens the valve B and closes the valve A. Oil is pumped through valve B and into the servomotor, thereby pushing the piston of the servomotor forwards. This in turn decreases the inlet area of the discharge into the turbine, thereby decreasing the speed. In both the cases mentioned above, the process continues until the normal position is reached.

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HYDRAULIC TURBINES Introduction: The device which converts h ydraulic energy into mechanical energy or vice versa is known as Hydraulic Machines . The h ydraulic machines which convert h ydraulic energy into mechanical energy are known as Turbines and that convert mechanical energy into h ydraulic energy is known as Pumps . Fig . shows a general layout of a h ydroelectric plant . Headrace hL Hg Penstock Turbine H Animation as in the PPT Tailrace Head hL H Hg Tail Race It consists of the following: 1 . A Dam constructed across a river or a channel to store water. The reservoir is also

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known as Headrace. 2 . Pipes of large diameter called Penstocks which carry water under pressure from storage reservoir to the turbines . These pipes are usuall y made of steel or reinforced concrete. 3 . Turbines having different t ypes of vanes or buckets or blades mounted on a wheel called runner. 4 . Tailrace which is a channel carrying water away from the turbine after the water has worked on the turbines . The water surface in the tailrace is also referred to as tailrace . Important Terms: Gross Head (H g ): It is the vertical difference between headrace and tailrace. Net Head:(H): Net head or effective head is the actual head available at the inlet of the to work on the turbine . H=Hg -hL Where h L is the total head loss during the transit of water from the headrace to tailrace which is m ainl y head loss due to friction, and is given b y hf  4 f LV 2 2gd Where f is the coefficient of friction of penstock depending on the type of material of penstock L is the total length of penstock V is the mean flow velocit y of water through the p enstock D is the diameter of penstock and g is the acceleration due to gravit y

Lecture Notes